Bahasa Indonesia (literally, language of Indonesia), also called Indonesian, the official language of Indonesia, is a remarkable language in several ways. To begin with, only a tiny fraction of the inhabitants of Indonesia speak it as a mother tongue[?]; for most people it is a second language. In a certain sense it is very modern: officially it came into being in 1945, and it is a dynamic language that is constantly absorbing new loanwords. Learning Indonesian can be a rewarding experience for a foreigner, as phonology and grammar are relatively simple. The rudiments that are necessary for basic everyday communication can be picked up in a few weeks.

Bahasa Indonesia is based on Malay, an Austronesian (or Malayo-Polynesian) language which had been used as a lingua franca in the Indonesian archipelago for centuries, and was elevated to the status of official language with the Indonesian declaration of independence in 1945. It is essentially the same language as Bahasa Malaysia, the official language of Malaysia. It is spoken as a mother tongue only by 7% of the population of Indonesia and 45% of the population of Malaysia, but all together almost 200 million people speak it as a second language with varying degrees of proficiency; it is an essential means of communication in a region with more than 300 native languages, used for business and administrative purposes, at all levels of education and in all mass media.

The Dutch colonization left an imprint on the language that can be seen in words such as polisi (police), kwalitas (quality), telpon (telephone), bis (bus), kopi (coffee), rokok (smoke) or universitas (university). There are also some words derived from Portuguese (sabun, soap; jendela, window) and from Arabic (khusus, special; maaf, sorry).

Indonesian is written in Latin script and is highly phonetical, especially since the spelling reform of 1972, which changed spellings based on the Dutch language, such as tj for the sound ch. Another spelling convention that goes back to the Dutch, the use of oe for the sound u, had already been eliminated in 1947, but still survives in proper names, for example Soeharto.

There are six pure vowel sounds: a (similar to the sound in bus), e (as in get), i (shorter than in eat), o (shorter than in dawn), u (as in put), and a neutral vowel like the second vowel of water which is also spelled e; and three diphthongs (ai, au, oi). The consonantic phonemes are rendered by the letters p, b, t, d, k, g, c (pronounced like the ch in cheese), j, h, ng (which also occurs initially), ny (as in canyon), m, n, s (unvoiced, as in sun or cats), w, l, r (trilled or flapped) and y. There are five more consonants that only appear in loanwords: f, v, sy (pronounced sh), z and kh (as in loch).

Compared with European languages, Indonesian is strikingly non-sexist. There is no grammatical gender, so the same word is used for he and she or for his and her. Most of the words that refer to people (family terms, professions, etc.) have a form that does not distinguish between the sexes; for example, adik can both refer to a (younger) brother or sister; there is no specific word for son or daughter, but only the equivalent of child; no distinction is made between girlfriend and boyfriend. In order to specify gender, an adjective has to be added: adik laki-laki corresponds to brother but really means male sibling. There is no word like the English man that can refer both to a male person and to a human being in general.

Plurals are expressed by means of reduplication, but only when not implied by the context; thus, orang-orang is people, but one thousand people is seribu orang, as the numeral makes it unnecessary to mark the plural form. (Reduplication has many other functions, however).

There are two forms of we, depending on whether you are including the person being talked to.

The basic word order is SVO. Verbs are not inflected for person or number, and there are no tenses; tense is denoted by time adverbs (such as yesterday) or by other tense indicators, such as sudah, meaning already. On the other hand, there is a complex system of verb prefixes to render nuances of meaning.